It is conventional in the manufacture of printed circuit boards to deposit a pattern of copper as a conductor onto the board, generally by an electroless process or a mixture of electroless and electrolytic processes, then to etch the copper pattern slightly to prepare it for electrolytic plating of tin/lead and then to plate a tin/lead layer onto the etched copper pattern. The term "tin/lead" is generally understood as mixtures of the metals either in a plating solution or plated onto a surface. At present, there are three etching systems used to etch the copper pattern prior to tin/lead plating: mixtures of sulfuric acid and hydrogen peroxide, mixtures of chromic and sulfuric acids and ammonium persulfate mixed with water or sulfuric acid or both. An exemplary process involves plating with copper, rinsing with water, etching with ammonium persulfate and sulfuric acid (or another of the above etchants) for about one to two minutes, rinsing with water, dipping in a 5% aqueous sulfuric acid solution, rinsing with water, dipping in a 10% fluoboric acid solution, rinsing with water and plating in a tin-lead bath. A recurring problem in such systems is that any sulfate remaining on the copper pattern when it enters the tin-lead bath causes poor adhesion of the tin-lead deposit on the copper pattern. If in subsequent processing, the deposit is either melted or reflowed, dewetting of the tin-lead layer will incur and an inferior printed circuit board will result.
Fluoboric acid is a known material for various steps in the processing of printed circuit boards, particularly as a dip step after the etching or as a component in the electrolytic plating bath. Fluoboric acid has not, however, been used previously as a component of the main copper etch, and, in fact, copper is virtually inert to fluoboric acid by itself under normal etching conditions.